NetworkVariable and NetworkList throw NullReferenceException if modified during shutdown

[A1win]

Description

When Shutdown() is called on the Server and a NetworkObject's OnNetworkDespawn causes a different NetworkObject to modify a NetworkList or NetworkVariable that's attached to it, a NullReferenceException is thrown.

For NetworkList.cs, the exception gets thrown in the MarkNetworkObjectDirty function on line 78.

For NetworkVariableBase.cs, it gets thrown on SetDirty function on line 98.

This didn't happen on NGO version 1.2.0. Could be dependant on script execution order somehow?

Reproduce Steps

1. Spawn NetworkObject A with a NetworkVariable attached to it.
2. Spawn NetworkObject B with a NetworkList attached to it.
3. Spawn NetworkObject C with an OnNetworkDespawn function that modifies the NetworkVariable of NetworkObject A.
4. Spawn NetworkObject D with an OnNetworkDespawn function that modifies the NetworkList of NetworkObject B.
5. Shut down the Server. Notice errors thrown by NetworkVariableBase.cs and NetworkList.cs.

I'm not sure if this is a reliable way to reproduce the issue and I don't currently have a small sample project to reproduce it in.

Actual Outcome

NetworkVariableBase and NetworkList cause a NullReferenceException when modified during server shutdown.

Expected Outcome

No exceptions are caused when modifying a NetworkVariable or a NetworkList during server shutdown.

Environment

• OS: Windows 10
• Unity Version: 2022.3.4f1
• Netcode Version: 1.5.1
• Netcode Commit: 7a969f8

[A1win]

A workaround I tried was to check for NetworkManager.ShutdownInProgress but looks like it sometimes returns true and sometimes false there.

[A1win]

@NoelStephensUnity Unfortunately, looks like this issue persists in Netcode 1.5.2 for both NetworkVariable and NetworkList as described above.

I'll report back once I know if the workaround of checking for NetworkManager.ShutdownInProgress now works consistently.

[A1win]

Looking further into this, on 1.5.1 the issue occurs whenever the server is shut down under the above circumstances. On 1.5.2, the error only appears when the application is shut down while the network is running (eg. closing the game window on Windows or exiting Play Mode in Unity Editor). This is not as critical since in theory nothing should break at that point anymore, but I assume still worth fixing.

[A1win]

@fluong6 @NoelStephensUnity This issue still occurs on 1.5.2 (3636884, Unity version 2022.3.7f1), but only when the application is shut down while the network is active, resulting in errors in the log and Editor console, but not causing any actual (apparent) issues for other clients/server. Checking for NetworkManager.ShutdownInProgress can be used as a workaround, but must be added as a check before every instance where a NetworkVariable or NetworkList is modified as a response to OnNetworkDespawned being called.